Are there options for interactive/dynamic content?

I'm starting to switch over to sage from mathematica, and so far the biggest thing I'm missing is the ability to make interactive applets. I managed to get mplh5canvas up and running. While it's a nice start, It's far from the sort of thing I can do with mathematica.

In mathematica, one can make an interactive sin graph with something like (I forget if the dynamic tag goes with the a or the plot[]):

Slider[Dynamic[a],{0,5}]
Plot[Dynamic[a]*sin[x],{x,-10,10}]

And of course it's even easier with Manipulate[].

How far is Sage from this sort of functionality? I think this sort of thing is immensely helpful to students who just want to explore a function.

If I learn how to effectively use the HTML 5 canvas and javascript, are dynamic plots within reach?